Enum RecordTransform 

pub enum RecordTransform {
    Flatten {
        separator: String,
    },
    RenameKeys {
        pattern: String,
        replacement: String,
    },
    KeysCase {
        mode: KeyCaseMode,
    },
    Select {
        fields: Vec<String>,
    },
    Drop {
        fields: Vec<String>,
    },
    Set {
        values: Map<String, Value>,
    },
    RenameField {
        fields: HashMap<String, String>,
    },
    Cast {
        fields: HashMap<String, CastType>,
        on_error: CastOnError,
    },
    Redact {
        fields: Vec<String>,
        mask: Value,
    },
    ValueCase {
        fields: Vec<String>,
        mode: ValueCaseMode,
    },
    SpellSymbols {
        extra: HashMap<String, String>,
        separator: String,
    },
    Custom(Arc<dyn Fn(Value) -> Value + Send + Sync>),
}

A transformation applied to every record fetched by a source (e.g. the REST source’s RestStream).

Transforms are applied in the order they are added via the owning source’s configuration (e.g. RestStreamConfig::add_transform).

The three built-in variants are each guarded by a Cargo feature flag (all enabled by default — see module-level docs). RecordTransform::Custom is always available and accepts any closure.

Variants

Flatten

Available on crate feature transform-flatten only.

Flatten nested JSON objects into a single-level map.

Nested key paths are joined with separator. Arrays are left as-is.

Requires feature transform-flatten (default).

Example

{"user": {"id": 1, "addr": {"city": "NYC"}}}  →  (separator = "__")
{"user__id": 1, "user__addr__city": "NYC"}

Fields

separator: String

RenameKeys

Available on crate feature transform-rename-keys only.

Apply a single regex substitution to every key in the record.

Keys in nested objects and objects inside arrays are also renamed recursively. pattern is a Rust regex; replacement may reference capture groups with $1, ${name}, etc. Chain multiple RenameKeys transforms for multi-step pipelines.

Requires feature transform-rename-keys (default).

Example

pattern = r"^_sdc_", replacement = ""   →   strip "_sdc_" prefix

Fields

pattern: String

replacement: String

KeysCase

Available on crate feature transform-keys-case only.

Re-case every key in the record according to mode.

Tokenises each key on whitespace, _, -, dropped punctuation, and lower→upper transitions, then re-joins in the requested convention. Walks recursively into nested objects and arrays. Two distinct keys that re-case to the same name error rather than silently overwriting.

Requires feature transform-keys-case (default).

Input	Snake	Camel	Pascal	Kebab	ScreamingSnake
"First Name"	"first_name"	"firstName"	"FirstName"	"first-name"	"FIRST_NAME"
"last-name"	"last_name"	"lastName"	"LastName"	"last-name"	"LAST_NAME"
"camelCase"	"camel_case"	"camelCase"	"CamelCase"	"camel-case"	"CAMEL_CASE"

Fields

mode: KeyCaseMode

Select

Available on crate feature transform-select only.

Keep only the listed top-level fields on each record; remove the rest.

Missing fields are silently skipped (they don’t introduce nulls). Non-object records pass through unchanged.

Requires feature transform-select.

Fields

fields: Vec<String>

Drop

Available on crate feature transform-drop only.

Remove the listed top-level fields from each record.

Missing fields are silently skipped. Non-object records pass through.

Requires feature transform-drop.

Fields

fields: Vec<String>

Set

Available on crate feature transform-set only.

Insert or overwrite top-level fields on each record with constant values.

Existing fields with the same name are overwritten. Non-object records pass through unchanged.

Requires feature transform-set.

Fields

values: Map<String, Value>

RenameField

Available on crate feature transform-rename-field only.

Exact-name rename of one or more top-level fields.

Unlike RecordTransform::RenameKeys (regex, recursive), this only touches exact top-level keys. Missing source fields are silently skipped. If a target name already exists on the record, the rename errors rather than silently overwriting.

Requires feature transform-rename-field.

Fields

fields: HashMap<String, String>

Map of old_name -> new_name.

Cast

Available on crate feature transform-cast only.

Coerce per-field types on each record.

Each named field is converted to the matching CastType. The CastOnError policy controls failure behaviour. Missing fields are silently skipped (no nulls introduced).

Requires feature transform-cast.

Fields

fields: HashMap<String, CastType>

on_error: CastOnError

Redact

Available on crate feature transform-redact only.

Replace each listed field’s value with a constant mask.

Missing fields are silently skipped (no mask inserted). Default mask is "***" when constructed from CLI config.

Requires feature transform-redact.

Fields

fields: Vec<String>

mask: Value

ValueCase

Available on crate feature transform-value-case only.

Lowercase / uppercase / trim string values on listed fields.

Non-string field values pass through unchanged. Missing fields are silently skipped.

Requires feature transform-value-case.

Fields

fields: Vec<String>

mode: ValueCaseMode

SpellSymbols

Available on crate feature transform-spell-symbols only.

Recursively spell out symbols inside every key with their word equivalents (% → percent, # → number, $ → dollar, …).

Built-in defaults cover the common ASCII symbols (see default_symbol_map); extra adds or overrides entries. Each replacement is surrounded by separator (default " ") so a chained RecordTransform::KeysCase picks up the word boundary. Keys are walked recursively into nested objects and arrays, mirroring the existing key-shape transforms. Two distinct keys that collapse to the same name error rather than silently overwriting.

Requires feature transform-spell-symbols.

Example

{"% sold": 1, "C# courses": 2}
  →  (defaults, separator=" ")
{" percent  sold": 1, "C number  courses": 2}

Fields

extra: HashMap<String, String>

Additional mappings (merged on top of default_symbol_map; entries with the same from override the default).

separator: String

Inserted around each replacement so word boundaries survive a downstream keys_case step. Default " ".

Custom(Arc<dyn Fn(Value) -> Value + Send + Sync>)

A user-supplied transformation function.

The function receives each record as a Value and returns the (possibly modified) record. Construct one with RecordTransform::custom.

Always available — not guarded by any feature flag.

Implementations

impl RecordTransform

pub fn custom<F>(f: F) -> RecordTransform

where F: Fn(Value) -> Value + Send + Sync + 'static,

Available on crate feature source-rest only.

Create a custom transform from any function or closure.

The closure receives each record as a Value and must return a Value (the transformed record). It is called once per record and may perform any manipulation — adding fields, removing fields, renaming, type coercion, etc.

Custom transforms are always available regardless of feature flags.

Example

use faucet_core::RecordTransform;
use serde_json::{Value, json};

// Inject a constant "source" field into every record.
let stamp = RecordTransform::custom(|mut record| {
    if let Value::Object(ref mut map) = record {
        map.insert("_source".to_string(), json!("my-api"));
    }
    record
});

Trait Implementations

impl Clone for RecordTransform

fn clone(&self) -> RecordTransform

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for RecordTransform

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.